Railguns are electrical guns known to accelerate projectiles along a pair of electrically conductive rails by permitting a large electric current to pass between the pair of rails by way of a conductive medium of, produced by, or otherwise associated with the projectile. This current interacts with the strong magnetic fields generated by the rails to accelerate the projectile using the same principles as the homopolar motor, and have been known to achieve velocities greater than what is typically achievable by conventional firearms-based technology. For example, railguns have been used in experiments to accelerate gram-sized and larger objects to speeds of 6 km/sec.
Various approaches are known for accelerating projectiles using railguns. One approach relies on a column of electrically conductive gas to produce a plasma armature to provide the propulsive force, in the form of gas pressure, to a non-conductive sabot typically made of a high-strength plastic, such as for example Lexan. It is appreciated that a plasma armature involves rail-to-rail plasma arcing. Other operating modes involve (1) using a solid conductor in contact with the rails for producing a solid armature, (2) using a transitioning hybrid armature which operates with both plasma arcing as well as conduction through a solid (plasma-solid-plasma conduction), and (3) tandem operation, which can involve both plasma armature and hybrid armature operation. It is notable, however, that plasma armatures have deleterious effects on railgun operation and projectile velocities, due to for example ablation drag, restrike, etc. Therefore plasma
One example railgun is shown in the article “The Gas-Insulated-Railgun” by Tidman, Parker, et. al., which uses a high-pressure gas fill in a steel tube. In this configuration a trailing wake can be produced, and at the wake boundary there is likely to be a region exactly at the “Paschen minimum”, i.e. where the value of pressure for the rail-to-rail gap at which the breakdown voltage is a minimum. This situation is likely to produce restrike arcs in the wake.
Another example is shown in the article “Railgun Performance with a Two-Stage Light-Gas Gun Injector” by Hawke, Suseoff, et. al., which involves a projectile-conforming sealed barrel design, along with a solid/hybrid transitioning armature. Because of the conforming barrel bore (i.e. barrel walls substantially conform to the cross-sectional profile of the projectile), it is typical in such designs that a plasma armature forms behind the hybrid armature (i.e. referred to as “tandem” operation). This is likely because the plasma cannot be completely contained within the hybrid and leaks rearward. The conforming barrel bore provides a means to support a non-zero plasma pressure and hence a non-zero plasma conductivity; the hot plasma in the rear of the armature providing a conductive path which inevitably leads to a plasma armature in the rear. In fact the experimental results show that tandem operation commences almost immediately. However, once a plasma armature forms in the back, all the deleterious effects of a plasma armature arise, i.e. ablation drag, restrike, etc.
And another example is described in the article “A Transitioning Hybrid Armature Concept” by Trevor James, which involves hybrid armature in a projectile conforming barrel bore, where the “plasma brushes” live in the “legs” of an otherwise “C-shaped” solid armature. The concept attempts to control the plasma armature pressure using radially-inward-directed “exhaust ducts”. This design is likely to operate in the “tandem” mode (hybrid armature plus plasma armature) at ultra-high-velocities, since the hot, conductive exhaust gases are directed rearward in a closed barrel, leading to tandem operation in a similar manner as in the Hawke, Suseoff article. For Ultra-High-Velocity operation tandem operation is not desirable for same reasons as discussed for the Hawke, Suseoff design.
As such, there is a need for a railgun designed to operate without and prevent the formation of plasma armatures, to enable high and ultra-high velocities in railgun applications.